Note: Descriptions are shown in the official language in which they were submitted.
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[0001] METHOD AND APPARATUS FOR ADJUSTING A
RESELECTION TIMER AND CELL RANKING
CRITERIA, AND REPORTING DEGRADED SIGNAL
MEASUREMENT OF A SERVING CELL
[0002] FIELD OF INVENTION
[0003] This application is related to wireless communications.
[0004] BACKGROUND
[0005] The third generation partnership project (3GPP) has recently
initiated the long ter`m evolution (LTE) program to bring new technology, new
network architecture and configurations, and new applications and services to
wireless cellular networks in order to provide improved spectral efficiency,
reduced latency, faster user experiences and richer applications and lower
cost
services. LTE aims at realizing an evolved universal terrestrial radio access
network (UTRAN). This concept applies to LTE and also applies to all other
universal mobile telecommunication system (UMTS) systems like release 99,
high speed downlink packet access (HSDPA), high speed uplink packet access
(HSUPA), high speed packet access (HSPA) enhancements, or any other releases.
[0006] In a UMTS system, when a WTRU is camped on a cell, the WTRU
regularly searches for a better cell according to a set of criteria. If a
better cell is
found, that cell is selected. In earlier UMTS systems, cell reselection can
per
performed while the WTRU is in one of an idle state, a radio resource control
(RRC) cell forward access channel (FACH) state and an RRC cell paging channel
(PCH) state. In LTE with only two states, LTE_idle and LTE_active, the WTRU
can perform cell reselection only in the LTE_idle state.
[0007] Reselection and handover are very different mechanisms.
Reselection is performed by the WTRU in an RRC_idle state. Handover is
performed by the WTRU in an RRC_connected state. Reselection is done
autonomously, (i.e., based on some parameters signaled by the network).
Handover is network controlled and directed.
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[0008] In previous UMTS systems, before the WTRU decides to camp on a
cell, it needs to check some basic criteria for the cell it is camping on.
Essentially, conditions for quality signal metric SQml > 0 and received signal
level
metric Sr,je,, > 0 need to be satisfied for the WTRU to camp on a cell, where
Sqõal
and Sr,aev are measured as:
SQõal = Ec/Io - Qqõalmin Equation (1)
where Ec is the channel code power of the cell and Io is the total
interference in
the cell. Thus, Eo/Io is a dimensionless ratio of the average power of a
channel,
(i.e., pilot channel), to the total signal power, and is measured by the WTRU.
Qquaimffi is the minimum required quality measure based on Ec/Io. Qqõalm;n is
extracted from a system information block 3 (SIB 3), which is broadcast by the
system, and
SrX1ev = RSCP - Qmievmin - max(WTRU-TXPWR_MAX R.ACH - P_MAX, 0),
Equation (2)
where received signal code power (RSCP) is measured by the WTRU, and
Qr,ae,m;I,
and WTRU_TXPWR_MAX RACH are transmitted in SIB 3. Qquaimin is the
minimum required quality measure based on EdIo, Qr,levmin is the minimum
required quality measure based on RSCP, and WTRU_TXPWR_MAX_RACH is
the maximum allowed uplink (UL) transmission (TX) power) of a random access
channel (RACH).
[0009] While in previous UMTS versions, the measurement quantity was
Ec/Io or RSCP, in LTE the measurement quantity is not yet decided. The
reference symbol received power (RSRP) is an LTE measurement that is
analogous to RSCP. The reference symbol received quality (RSRQ) is also an
LTE measurement that is analogous to EdIo.
[0010] In addition to Qqu.1mcn, Qr,aeõmin and WTRU_TXPWR_MAX RACH,
the following other parameters are transmitted in SIB 3 for cell reselection:
1) Sitr.rcn (optional): The WTRU measures intra-frequency neighbor cells
when Squal, as defmed by Equation (1), is less than or equal to Sitr~r6. If
S;ntr..b
is not specified by the network, the WTRU always measures intra-frequency
neighbor cells.
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2) Sintersrch (optional): The WTRU measures inter-frequency neighbor cells
when Sqõal, as defined by Equation (1), is less than or equal to Sinte,srch.
If Sintersrch
is not specified by the network, the WTRU always measures inter-frequency
neighbor cells
3) SSearChxAT (optional): The WTRU measures inter-RAT neighbor cells when
SQual, as defmed by Equation (1), is less than or equal to SseardnxAT. If
SsearchxnT iS
not specified by the network, the WTRU always measures inter-RAT neighbor
cells. Always measure inter-RAT neighbor cells when not specified.
4) QhYstls: This is a hysteresis value added to the serving cell signal
quality, (as
measured by RSCP), to increase the rank of the serving cell.
5) QhYst2s: This is a hysteresis value added to the serving cell signal
quality, (as
measured by Eo/Ia), to increase the rank of the serving cell.
6) Tresei: The time for which the neighbor cell should meet cell reselection
criteria before the WTRU reselects to the neighbor cell.
[0011] The following are some of the important parameters transmitted in
SIB 11:
1) Neighbor cell list (NCL).
2) Qoffsetls: Quality offset used to rank the serving cell based on RSCP.
3) Qoffset2s: Quality offset used to rank the serving cell based on E,/Io.
4) WTRU_TXPWR_MAX_RACH: Maximum allowed UL TX power for
neighbor cell.
5) QQõdmi : Minimum required quality measure based on Ea/Io.
6) Qr,aevmin: Minimum required quality measure based on RSCP.
[0012] Using these parameters, the WTRU is able to rank its serving and
neighbor cells. Serving cell ranking is given as:
Rank_s = Eo/Io + Qhyst2 + Qoffmbms. Equation (3)
[0013] The signaled value Qoffmbms is an offset added to those cells (serving
or neighboring) belonging to the multimedia broadcast/multimedia service
preferred layer (MBMS PL).
As mentioned above, Qhy-t2s is a static parameter indicated by the network to
the
WTRU in SIB 3 in the current UMTS systems for ranking of the serving cell.
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[0014] Neighbor cell ranking is given as:
NRank_n = EdIo - Qoffset2 + Qoffibms Equation (4)
[0015] A ranking equation similar to Equation (4) may be applied when the
measurement quantity is RSCP. For a particular cell to be reselected, the
neighbor cell ranking has to be above the serving cell ranking for a period
equal
to Tresei. Even if the ranking of the serving cell falls rapidly, neither the
ranking
nor the value Tresei of a reselection timer is modified to reselect to the
neighbor
cell at a faster rate.
[0016] Other than the reselection criteria, a scalability factor for the high
mobility state, (i.e., the WTRU is moving at a high speed) may be implemented.
Accordingly, when the number of cell reselections that occur during a
particular
time period TcRm. exceeds a value NCR, a high mobility state has been
detected.
When a high mobility state is detected, the reselection timer value Tresel is
multiplied by a scalability factor, if the scalability factor is signaled by
the
network as an optional parameter in SIB 3, depending on whether an intra or
inter-frequency selection, or an inter-RAT selection, is being implemented.
[0017] There are many scenarios under which the above mobility condition
would not be effective. For example, the WTRU may be in a fade from the
serving cell, and not in a mobility scenario. In such a case, the WTRU may not
be able to sustain a call and it would need to more rapidly reselect to the
neighbor cell to prevent it from going out of service in the idle state, or to
prevent
the WTRU from losing data in other states, such as a FACH state.
[0018] Alternatively, the WTRU could be in high mobility scenario, but
across a single large cell, so it might not meet the existing criteria of cell
reselections. The serving cell could be dropping rapidly in such a case and
again
the WTRU would need to reselect to the neighbor cell quickly.
[0019] Alternatively, the WTRU may take a long time to reselect to a cell
due to taking an extended time period to read the SIBs, or the WTRU may have
gone out of service between cell reselections because the serving cell signal
quality fell rapidly before the WTRU could reselect to another cell, in which
case
the WTRU may not even meet the criteria for a high mobility.
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[0020] When the WTRU is in an active state, it needs to do a handover to a
neighbor cell. In UMTS systems, this could either be a soft handover or a hard
handover. In LTE, the WTRU is only allowed to do a hard handover.
[0021] In active state, the WTRU always measures the cells in its neighbor
list which is sent in SIB 11 or in the measurement control message. If a
neighbor
list is truncated or removed as is being discussed in LTE, the WTRU could also
search and detect neighboring cells and perform measurements on them.
[0022] When the neighbor cell exceeds a reporting range threshold, or
meets an entry criteria, the WTRU initiates a time-to-trigger (TTT) that
defines
the minimum amount of time that the WTRU needs to wait before it can send a
measurement report. A TTT timer may be used to establish the duration of the
TTT. The TTT is specified in the SIB or measurement control message for each
event. If the TTT expires and the neighbor cell remained above the threshold
during the entire duration of a TTT, then a measurement report is triggered
with
the appropriate event. The network then responds with an active set update
(ASU) or a handover command. If, during the TTT, the neighbor cell signal
measurement, (e.g., signal strength, signal quality), falls below a
preconfigured
signal quality, then the TTT is terminated for that neighbor cell. The
neighbor
cell needs to return over the entry criteria for the WTRU to start
measurements
on the cell again.
[0023] If during the process, the serving cell signal rapidly fades, or the
quality of the serving cell signal degrades, then the WTRU may not be in a
position to receive the ASU or the handover command from the network. Also,
the neighbor cell may fluctuate slightly above and below the threshold,
causing
the WTRU to start and stop the TTT. Hence, the WTRU may never manage to
trigger the measurement report to reselect a neighbor cell.
[0024] In UMTS systems with soft handover, this problem is not seen
predominantly. However, in LTE with no soft handovers, this problem may be
more predominant. Thus, a more robust handover scheme that considers the
WTRU serving cell condition is desired.
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[0025] SUMMARY
[0026] Various methods for overcoming the drawbacks of existing WTRU
speed detection mechanisms in UMTS are disclosed. Existing WTRU speed
detection mechanisms, and the way they are applied from UMTS, are not
sufficient. Thus, signal measurement, (e.g., signal strength, signal quality),
is
used to overcome the drawbacks of the existing WTRU speed detection
mechanisms. Correspondingly, some reselection parameters such as the
hysteresis value and the time value T,esel of the reselection timer are
modified.
Also, the hysteresis quality value may be scaled by the existing WTRU speed
detection techniques in UMTS. For handover, there may be scenarios where it is
required to perform a serving signal measurement and modify the TTT. Thus,
the TTT is modified according to WTRU speed since serving signal measurement
correlates to WTRU speed.
[0027] A wireless communication method of adjusting the ranking criteria
of a serving cell associated with a WTRU is disclosed herein. A signal
measurement, (e.g., RSRQ, RSCP, RSRP), of the serving cell is performed. A
serving cell hysteresis value is set to a first value if the signal
measurement of
the serving cell exceeds a first threshold. The serving cell hysteresis value
is set
to a second value if the signal measurement of the serving cell is less that
the
first threshold and is greater than a second threshold for a first time
interval.
The serving cell hysteresis value is set to a third value if the signal
measurement
of the serving cell is less than the second threshold for a second time
interval.
The ranking criteria of the serving cell is adjusted based on the serving cell
hysteresis value after being set to one of the first value, the second value
and the
third value.
[0028] A wireless communication method of adjusting the ranking criteria
of a neighbor cell associated with a WTRU is also disclosed herein. A signal
measurement, (e.g., RSRQ, RSCP, RSRP), of the serving cell is performed. A
neighbor cell offset value is set to a first value if the signal measurement
of the
serving cell exceeds a first threshold. The neighbor cell offset value is set
to a
second value if the signal measurement of the serving cell is less that the
first
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threshold and is greater than a second threshold for a first time interval.
The
neighbor cell offset value is set to a third value if the signal measurement
of the
serving cell is less than the second threshold for a second time interval. The
ranking criteria of the neighbor cell is adjusted based on the neighbor cell
offset
value after being set to one of the first value, the second value and the
third
value.
[0029] A wireless communication method of adjusting the ranking criteria
of a serving cell associated with a WTRU is also disclosed herein. A
reselection
timer in the WTRU is set to a first value. A hysteresis value is set to a
second
value. A number of cell reselections associated with the WTRU that occur
during
a predetermined time period are monitored. Mobility factors associated with
the
WTRU are monitored. A determination is made as to whether to adjust the
reselection timer by multiplying the first value with a first scaling factor,
and/or
adjust the ranking criteria of the serving cell by multiplying the second
value of
the hysteresis value with a second scaling factor, to reduce the ranking of
the
serving cell, if the number of cell reselections exceeds a third value, and a
high
mobility factor is detected.
[0030] A wireless communication method of adjusting a reselection timer in
a WTRU is also disclosed herein. A signal measurement, (e.g., RSRQ, RSCP,
RSRP), of the serving cell is performed. A reselection timer in the WTRU is
set to
a first value if the signal measurement of the serving cell exceeds a first
threshold. The reselection timer is set to a second value if the signal
measurement of the serving cell is less that the first threshold and is
greater
than a second threshold for a first time interval. The reselection timer is
set to a
third value if the signal measurement of the serving cell is less than the
second
threshold for a second time interval.
[0031] A cell signal measurement reporting method performed by a WTRU
is also disclosed herein. A serving cell signal measurement and a neighbor
cell
signal measurement are performed. A TTT interval is started when the neighbor
cell signal measurement rises above a reporting range threshold. If the
serving
cell signal measurement falls below a serving cell threshold, a measurement
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report is transmitted before the expiration of the TTT interval reporting that
the
serving cell signal measurement has fallen below the serving cell threshold
and
providing information about the neighbor cell used to generate a handover
command. Alternatively, if the serving cell signal measurement falls below a
serving cell threshold and stays below the threshold during a predetermined
time
interval, a measurement report is transmitted during the TTT interval
reporting
that the serving cell signal measurement has fallen below the serving cell
threshold and providing information about the neighbor cell used to generate a
handover command.
[0032] BRIEF DESCRIPTION OF THE DRAWINGS
[0033] A more detailed understanding may be had from the following
description, given by way of example in conjunction with the accompanying
drawings wherein:
[0034] Figure 1 shows the variation of various signals with time and other
quantities used in handover decisions;
[0035] Figure 2 is a flow diagram of a cell reselection process;
[0036] Figure 3 is a flow diagram of a handover procedure using TTT
scaling;
[0037] Figure 4 shows an example of the configuration of a WTRU used to
perform the methods disclosed herein;
[0038] Figure 5 is a flow diagram of a wireless communication method of
adjusting the ranking criteria of a serving cell associated with a WTRU;
[0039] Figure 6 is a flow diagram of a wireless communication method of
adjusting the ranking criteria of a neighbor cell associated with a WTRU;
[0040] Figure 7 is a flow diagram of a wireless communication method of
adjusting the ranking criteria of a serving cell associated with a WTRU;
[0041] Figure 8 is a flow diagram of a wireless communication method of
adjusting a reselection timer in a WTRU; and
[0042] Figures 9 and 10 are flow diagrams of cell signal measurement
reporting methods performed by a WTRU.
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[0043] DETAILED DESCRIPTION
[0044] When referred to hereafter, the terminology "wireless
transmit/receive unit (WTRU)" includes but is not limited to a user equipment
(UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular
telephone, a personal digital assistant (PDA), a computer, or any other type
of user device capable of operating in a wireless environment.
[0045] When referred to hereafter, the terminology "base station" includes
but is not limited to a Node-B, a site controller, an access point (AP), or
any other
type of interfacing device capable of operating in a wireless environment.
[0046] In a first wireless communication method disclosed herein, LTE is
the system focused upon, and RSRQ and RSRP are used as measurement
quantities. Alternatively, other measurement quantities could be chosen
without
affecting the invention. The following may be applied to both current UMTS
systems and LTE.
[0047] Qhystls is a hysteresis value that is signaled. In the following
method, this hysteresis value is scaled and a new hysteresis value called
Qh,.st is
introduced, which is based on a serving signal measurement, (RSRQ, RSCP,
RSRP), which in turn is a measure of mobility.
[0048] A situation may arise in which the serving cell signal quality may
fall too rapidly before the cell reselection occurs, or the criteria for high
mobility
might not be met. Thus, the WTRU would suffer from cell reselection failures.
This problem may be addressed by taking the serving cell quality into account
while doing cell reselection. While the criteria for camping on a cell may
remain
the same as in previous systems or be modified, modification of the ranking
criteria itself and the reselection timer will now be disclosed.
[0049] Many variations for ranking the serving and neighbor cell are
possible. Note that all equations below use the measurement quantity RSRQ,
which as mentioned before is assumed to be analogous to EdIo. A similar set of
equations can be written with the measurement quantity RSRP, which as
mentioned before is assumed to be analogous to RSCP. Note that in the
equations below, the quantity RSRQ may be substituted by any other suitable
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"signal quality" measure, while the quantity RSCP may be by any other suitable
"signal level" measure, or any other suitable measures.
[0050] For a serving cell, the ranking criteria is kept the same, namely:
Rank_s = RSRQs + Qh,.st2s + Qoffinbms, Equation (5)
where RSRQS is the reference symbol received quality of the serving cell.
[0051] For a neighbor cell, however, the ranking criteria is modified as:
Rank_n = RSRQn - Min(Qeffset2, Qhyst) + Qoffmbms, Equation (6)
where RSRQn is the reference symbol received quality of neighbor cell n,
or in general,
Rank_n = function (RSRQn, Qoffsetz, Qoffmbms, RSRQS). Equation (7)
[0052] By making Rank n a function that is adapted based on RSRQS, we
enhance the ranking criteria and avoid the potential problems of the existing
cell
reselection scheme.
[0053] An additional parameter may be introduced called QhYst which is
applied by the WTRU as follows:
If RSRQs > x, Equation(8)
where x is a serving cell signal measurement threshold,
QhyF,t = zl dB; Equation(9)
Else if for a time interval T11, If x> RSRQs > y; Equation(10)
where T11 is a timer value which indicates the interval of time during which
RSRQ has to be between the 2 thresholds x and y.
Qh~,t = z3 dB. Equation(11)
Else, if RSRQs < y for a time interval T12, Equation(12)
Qhpt = z2 dB, Equation(13)
where zl > z3 > z2 and x > y.
[0054] The values x, y, zl, z2, z3, Til, and T12 may either be
implementation dependent, network defined or defined in standard after
simulation results. Tli and T12 are the intervals of time for which the
conditions
for RSRQ have to be satisfied. The serving cell thresholds or Qbyst values may
be
communicated dynamically via RRC messages, (e.g., in one or more SIBs).
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[0055] When the WTRU serving cell signal measurement is below a
threshold, the neighboring cell rank is improved by subtracting a lower value
from the measurement quantity, which in this case is RSRQ. If the serving cell
signal measurement is above a threshold, then the value Qoffset2 or the
quantities
zl or z3 may still be subtracted, depending on the threshold and depending on
the values of z 1 and z3. For the algorithm to work effectively, z2 must be at
least
less than Qoffset2.
[0056] Alternatively, we could have a two-level threshold where, above a
value x, we can use a similar hysteresis value as used today in UMTS systems,
or
use a new hysteresis value zl. If the signal strength of the WTRU falls below
a
value x for a time interval T13, a Qhyst value z2 may be used. Alternatively,
instead of network signaling a new value x, the WTRU could use one of the
existing thresholds, such as QQualm;n, for the value x and the network in such
a
case would not need to signal any new thresholds. Also, for the time interval
T13,
the WTRU may use one of the existing time interval values signaled by the
network and possibly a new time interval value T13 may not need to be signaled
by the network.
[0057] Alternatively, instead of defining different values, a network could
signal one value (say zl) and the scalability value along with it helping the
WTRU calculate z2 and z3.
[0058] Alternatively, instead of three levels, n levels could be used, where
n>2 where the thresholds could again either be implementation dependent or
network defined or defined in standard after simulation results. The
thresholds
may be communicated dynamically via RRC messages, (e.g., in one or more SIBs)
[0059] Alternatively, the equations disclosed above can also be written as
follows:
For serving cell the ranking criteria is modified as:
Rank s= RSRQS + Min(QhYst2, Qhyt) + Qoffmbms. Equation(14)
For neighbor cell, the cell ranking is kept the same:
Rank_n = RSRQn - Qoffset2 + Qoffinbms. Equation(15)
The calculation of Qhpt would be the same as mentioned above.
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[0060] Alternatively, the value Qt,yst2 or Qoffset2 could be eliminated and
the
equations written as:
For serving cell the ranking criteria can be kept the same:
Rank_s = RSRQs + QhYst2 + Qoffinbms. Equation(16)
For neighbor cell though, the ranking criteria are modified as:
Rank_n = RSRQn - Qhyst + Qoffinbms. Equation(17)
The calculation of Qhyst would be the same as mentioned above.
[0061] Alternatively, for serving cell the ranking criteria can be modified
as:
Rank_s = RSRQs + Qhyst + Qoffmbms. Equation(18)
For neighbor cell, keep the cell ranking the same:
Rank_n = RSRQn - Qoffset2 + Qoffinbms. Equation(19)
The calculation of Qhyst is then the same as mentioned above.
[0062] A similar set of the equations with the parameter Qt,yst can be
applied when the measurement parameter is RSRP.
[0063] Even though the above equations are for non-hierarchical cell
structure (HCS), the parameter QhYst could also be applied to the equations
when
HCS are used.
[0064] Note that in the previous equations, the desired the effect of MBMS
could be neutralized by setting Qoffmbms to 0, (e.g., in case there is no MBMS
service, or if one does not want to consider it in the cell reselection
criteria).
[0065] Alternatively or in addition, it is disclosed that when the number of
cell reselections during some time period TCRmax exceeds a value NCR, and a
high
mobility factor is detected, instead of just multiplying the Tresel with a
scaling
factor as in current UMTS systems, it is proposed to also have the option of
multiplying the Qi,yFt value by a scaling factor to reduce the rank of the
serving
cell. This multiplication of Qhyst value with the scaling factor could be done
in
addition to multiplying the Tresel value with the scaling factor or only one
of them
could be multiplied with the scaling which may be decided by the WTRU itself,
depending on a factor such as radio condition, or could be signaled by the
network
which may be cell dependent, or based on any other factor. This scaling factor
for
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Qhysc may either be the same as that used for Tresel, or another scaling
factor for
multiplying with the QhYsc value may be signaled.
[0066] For the Tresel time interval, a multilevel reselection timer performs
as follows:
If RSRQs > x, then the value of the Tresel (reselection timer) that could be
used may be the same as the value of a reselection timer that is currently
used in
UMTS systems, (i.e., no scaling is required).
Else, if x>RSRQs > y for a time interval T14, Tresel is reduced to a value z3.
Else, if RSRQs < y if for a time interval T15, Tresel= 0 or a very small value
z2, where zl>z3>z2 and x>y.
[0067] The values x, y, zl, z2, z3, T14, and T15 could either be
implementation dependent or network defined or defined in standard after
simulation results. Time intervals T14 and T15 are the intervals for time for
which
the conditions for RSRQ have to be satisfied. They may be communicated
dynamically via RRC messages, (e.g., in one or more SIBs).
[0068] In general, reselection timer adapted and made a function of RSRQs:
Tresel = function (RSRQg).
[0069] As seen, depending on the strength of the WTRU serving cell, Tresel
timer is reduced for faster reselection to a neighbor cell.
[0070] Alternatively, there could be a two level threshold where above a
value x, we could use a similar Tresel timer as current UMTS systems or a new
reselection timer z 1, and if the signal strength of the WTRU falls below the
value
x for a time interval T16, either a shortened Tresel timer or no reselection
timer is
used at all. Alternatively, instead of network signaling a new value x, the
WTRU
could use one of the current thresholds as signaled today like QQudm;n for the
value x and network in such a case would not need to signal any new
thresholds.
Also, for the time interval T16, the WTRU could use one of the existing timer
values signaled by the network and possibly a new time interval value T16 may
not need to be signaled by the network. The time intervals T14, T15 and T16
may
be the same as the time intervals Tll, T12 and Tis, or they may be different.
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[0071] Alternatively, instead of defming different values, a network could
signal one value (say zl) and the scalability value along with it to help the
WTRU calculate z2 and z3.
[0072] Alternatively, instead of 2 or 3 levels, there could be n levels where
n>=2 where the thresholds could again either be implementation dependent or
network defined or defined in standard after simulation results. The
thresholds
or timer values may be communicated dynamically via RRC messages (e.g., in
one or more SIBs).
[0073] Either the network or the WTRU could decide to use both the
adaptive ranking criteria and the reselection timer or either one alone for
more
robust cell reselection.
[0074] For the adaptive reselection idea based on signal strength disclosed
here, the multiplication of Qt,ysc value with the scaling factor could be done
in
addition to multiplying the Tresei value with the scaling factor or only one
of them
could be multiplied with the scaling factor which may be decided by the WTRU
itself, depending on a factor such as a radio condition, or may be signaled by
the
network, which could be cell dependent, or based on any other factor. This
scaling factor for Qi,Yst may either be the same as that used for Tresel, or
another
scaling factor for multiplying with the Qhyst value may be signaled. Also, the
scaling factor signaled for the adaptive reselection method proposed above may
be same as what is currently signaled for a high mobility scenario, or another
scaling factor to be used specifically for adaptive reselection based on
signal
strength could be signaled.
[0075] The following describes the mitigation of a handover failure caused
by the serving cell falling too rapidly, in which the serving cell quality is
taken
into account during the handover procedure.
[0076] In Figure 1, a timeline for triggering a measurement report for a
serving cell signal measurement falling below a threshold is shown, where the
following are assumed:
[0077] Signal measurement, (e.g., RSRQ, RSCP, RSRP), of the serving cell
over time.
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[0078] Signal measurement, (e.g., RSRQ, RSCP, RSRP), of the neighbor cell
over time.
[0079] Serving cell threshold x: A threshold below which the serving cell
sends a measurement report to the network.
[0080] Reporting Range: Value above which the TTT interval on the
neighbor cell is started.
[0081] Time T1: Time when the neighbor cell rises above the reporting
range to start a TTT interval.
[0082] Time T2: Time when the signal measurement of the serving cell falls
below the serving cell threshold x and sends a measurement report to the
network reporting that the serving cell signal measurement has fallen below
the
threshold and giving information about the neighbor cell on which the TTT
interval is counting down.
[0083] Alternatively, instead of the value T2, a time interval T4, (not
shown in Figure 1), may be used as the amount of time the serving cell signal
measurement may need to be below the serving cell threshold x. Thus, when the
serving cell has been a particular threshold for the duration of the time
interval
T4, the WTRU may send a measurement report. Furthermore, the serving cell
threshold may be one of the values already transmitted in the SIB, such as
Qqu~mi., or the serving cell signal threshold may be transmitted separately
either
through a broadcast message or part of some dedicated RRC measurement
control message.
[0084] Time T3: Time when the TTT interval has expired and the WTRU
can report a measurement report to the network as before.
[0085] As seen in Figure 1, when the neighbor cell signal measurement
rises above the reporting range, the WTRU can start the TTT interval for the
neighbor cell. During the running of TTT interval, if the serving cell signal
measurement falls below a serving cell threshold x, the WTRU can send a
measurement report before the expiration of the TTT interval, reporting that
the
serving cell signal measurement has fallen below the threshold x. The
measurement report would also identify the neighbor cell on which the TTT
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interval is counting down, thereby requesting the network to generate a
handover command immediately to hasten a handover.
[0086] Alternatively, after starting the TTT interval, the WTRU can send a
measurement report that indicates that the serving cell signal measurement has
fallen below the serving cell threshold x and identifies the neighbor cell on
which
the TTT interval is counting down, thereby requesting the network to send the
handover command immediately to hasten the handover, if the serving cell
signal
measurement falls and remains below the serving cell threshold x for a time
interval T4. If no handover command is received, and if the TTT interval
expires
with the neighbor cell having remained above the reporting range during the
entire duration of the TTT interval, a measurement report is triggered with
the
appropriate event. For example, when the neighbor cell is added to an active
set,
and a handover command is received, the WTRU can stop its TTT interval and
perform a handover procedure.
[0087] Alternatively, if no neighbor cell has met the reporting criteria, or
if
the neighbor cell signal measurement falls below the exit criteria during the
duration of the TTT interval and the serving cell signal measurement falls
below
a threshold, the WTRU can still send a measurement report to the network
reporting that the serving cell signal measurement has fallen below the
threshold. The network may then use this information to perform a blind
handover, or send a signal to the WTRU reducing the TTT interval and/or
lowering the reporting range, or in any manner that it deems appropriate for
that
WTRU/scenario.
[0088] The serving cell threshold may be sent by the network in the SIB or
measurement control message, or in any other message, or could be determined
by the WTRU or may be mentioned in the standards based on simulation results.
[0089] The principles of adaptively sending a measurement report based on
the serving cell threshold before the expiration of the TTT interval may be
applied to intra-frequency and/or inter-frequency and/or inter-RAT handovers.
[0090] If the serving cell signal measurement is falling too rapidly, or the
TTT interval is too long and the serving cell quality is degrading, a call can
be
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ITC-2-l626.01.'VV0'----
REPLf ~CEMENT STMET
saved using the methods and apparatus described above. Furthermore, by
using an adaptive cell reselection-and handover procedure, the WTRIJ is more
likely to maintain service and sustain a call during a cell reselection and
handover procedure.
[0091] Figure 2 is a flow di:igram of a cell reselection process 200. The
cell reselection process starts at: step 205. At step 210, a determination is
made as to what the serving eeL signal measurement and/or the number of
cell reselectioia$ is, (WTRU xnotility detection). If the serving cell signal
measurement is low and/or the n~-mber of cell reselections is high, indicating
a
high mobility, the Qi,yst andJor the Trasez are scaled at step 215 with the
same or
different scaling factors, (i.e., the ' parameters are scaled to a low value).
If the
serving cell signal xneasurement. and/or the number of cell reselections is
medium., in.dice.ti-ng average mob',Jity, the Qhyst and/or the TYQe,I are
scaled at
-
step 220 with the same or differrmt scaling factors, (i.e., the parameters are
scaled to a medium value). If the serving cell signal measurement is high
an,dlor the numk-er of cell reselections is low, indicating low mobility, the
Q6,d
and/or the Tr~aei are scaled at s~;ep 225 with the same or different scaling
factors, (i.e., the parameters are: scaled to the value signaled, or it is
left
unchanged)_ In step 230, the ce:l reselection equations are applied with the
correct values of Qhyt and Treeel, 6 epending on the state of the WTRU. In
step
235, the cell reselection process '6.00 ends by reselection to the desired
aell as
indica.ted by the reselection equatious.
[0092] Figure 3 is a flow c;iagram of a handover procedure 300 using
TTT scaling. In step $45, the TTT interval is started when the signal
measurement of a neighbor cell r:,ses above a serving cell signal threshold.
In
step 310, a serving cell signal measurement is performed, (WTRU speed
detection). In step 315, if the ser.vvi.n.g cell signal measurement falls
below the
serving cell signal threshold, or zvays below a serving cell signal threshold
for
a predetermined time period, the TTT interval is reduced/scaled (step 320).
Otherwise, the sigzxal,ed value of the TTT interval is maintained (step 325).
In
step 330, a measurement report. is sent when the TTT interval expires to
generate a handover comm.and.
AMENDED SHEET
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[0093] Figure 4 shows an example of the configuration of a WTRU 400 used
to perform the methods disclosed herein. The WTRU 400 includes a transmitter
405, a receiver 410, an antenna 415, a processor 420, a reselection timer 425
and
a TTT timer 430.
[0094] The receiver 410 is configured to perform a signal measurement,
(e.g., RSRQ, RSCP, RSRP), of a serving cell. The processor 420 is configured
to
set a serving cell hysteresis value to a first value if the signal measurement
of
the serving cell exceeds a first threshold, set the serving cell hysteresis
value to a
second value if the signal measurement of the serving cell is less that the
first
threshold and is greater than a second threshold for a first time interval,
set the
serving cell hysteresis value to a third value if the signal measurement of
the
serving cell is less than the second threshold for a second time interval, and
adjust the ranking criteria of the serving cell based on the serving cell
hysteresis
value after being set to one of the first value, the second value and the
third
value.
[0095] The receiver 410 is further configured to perform a signal
measurement, (e.g., RSRQ, RSCP, RSRP), of a serving cell. The processor 420 is
configured to set a neighbor cell offset value to a first value if the signal
measurement of the serving cell exceeds a first threshold, set the neighbor
cell
offset value to a second value if the signal measurement of the serving cell
is less
that the first threshold and is greater than a second threshold for a first
time
interval, set the neighbor cell offset value to a third value if the signal
measurement of the serving cell is less than the second threshold for a second
time interval, and adjust the ranking criteria of the neighbor cell based on
the
neighbor cell offset value after being set to one of the first value, the
second value
and the third value.
[0096] The processor 420 is further configured to set the reselection timer
425
to a first value if the signal measurement of the serving cell exceeds a first
threshold, set the reselection timer 425 to a second value if the signal
measurement of the serving cell is less that the first threshold and is
greater
than a second threshold for a first time interval, and set the reselection
timer 425
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to a third value if the signal measurement of the serving cell is less than
the
second threshold for a second time interval.
[0097] The receiver 410 is further configured to perform a serving cell signal
measurement and a neighbor cell signal measurement. The processor 420 is
further configured to start a TTT interval established by the TTT timer 430
when
the neighbor cell signal measurement rises above a reporting range threshold
and adjust the TTT interval. The transmitter 405 is configured to transmit a
measurement report before the expiration of the TTT interval if the serving
cell
signal measurement falls below a serving cell threshold, the measurement
report
indicating that the serving cell signal measurement has fallen below the
serving
cell threshold and provide information about the neighbor cell used to
generate a
handover command. The transmitter 405 is further configured to transmit a
measurement report during the TTT interval if the serving cell signal
measurement falls below a serving cell threshold and stays below the threshold
during a predetermined time interval.
[0098] Figure 5 is a flow diagram of a wireless communication method 500 of
adjusting the ranking criteria of a serving cell associated with a WTRU. In
step
505, a signal measurement, (e.g., RSRQ, RSCP, RSRP), of the serving cell is
performed. In step 510, a serving cell hysteresis value is set to a first
value if the
signal measurement of the serving cell exceeds a first threshold. In step 515,
the
serving cell hysteresis value is set to a second value if the signal
measurement of
the serving cell is less that the first threshold and is greater than a second
threshold for a first time interval. In step 520, the serving cell hysteresis
value is
set to a third value if the signal measurement of the serving cell is less
than the
second threshold for a second time interval. In step 525, the ranking criteria
of
the serving cell is adjusted based on the serving cell hysteresis value after
being
set to one of the first value, the second value and the third value.
[0099] Figure 6 is a flow diagram of a wireless communication method 600 of
adjusting the ranking criteria of a neighbor cell associated with a WTRU. In
step
605, a signal measurement, (e.g., RSRQ, RSCP, RSRP), of the serving cell is
performed. In step 610, a neighbor cell offset value is set to. a first value
if the
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signal measurement of the serving cell exceeds a first threshold. In step 615,
the
neighbor cell offset value is set to a second value if the signal measurement
of the
serving cell is less that the first threshold and is greater than a second
threshold
for a first time interval. In step 620, the neighbor cell offset value is set
to a
third value if the signal measurement of the serving cell is less than the
second
threshold for a second time interval. In step 625, the ranking criteria of the
neighbor cell is adjusted based on the neighbor cell offset value after being
set to
one of the first value, the second value and the third value.
[0100] Figure 7 is a flow diagram of a wireless communication method 700 of
adjusting the ranking criteria of a serving cell associated with a WTRU. In
step
705, a reselection timer in the WTRU is set to a first value. In step 710, a
hysteresis value is set to a second value. In step 715, a number of cell
reselections associated with the WTRU that occur during a predetermined time
period are monitored. In step 720, mobility factors associated with the WTRU
are monitored. In step 725, if the number of cell reselections exceeds a third
value, and a high mobility factor is detected, a determination is made as to
whether a first adjustment of the reselection timer should be performed by
multiplying the first value with a first scaling factor, a second adjustment
of the
ranking criteria of the serving cell should be performed by multiplying the
second
value of the hysteresis value with a second scaling factor, or both of the
first and
second adjustments should be performed, to reduce the ranking of the serving
cell.
[0101] Figure 8 is a flow diagram of a wireless communication method 800 of
adjusting a reselection timer in a WTRU. In step 805, a signal measurement,
(e.g., RSRQ, RSCP, RSRP), of a serving cell is performed by the WTRU. In step
810, a reselection timer in the WTRU is set to a first value if the signal
measurement of the serving cell exceeds a first threshold. In step 815, the
reselection timer is set to a second value if the signal measurement of the
serving
cell is less that the first threshold and is greater than a second threshold
for a
first time interval. In step 820, the reselection timer is set to a third
value if the
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signal measurement of the serving cell is less than the second threshold for a
second time interval.
[0102] Figure 9 is a flow diagram of a cell signal measurement reporting
method 900 performed by a WTRU. In step 905, a serving cell signal
measurement is performed. In step 910, a neighbor cell signal measurement is
performed. In step 915, a TTT interval is started when the neighbor cell
signal
measurement rises above a reporting range threshold. In step 920, if the
serving
cell signal measurement falls below a serving cell threshold, the TTT interval
is
adjusted and a measurement report is transmitted before the expiration of the
TTT interval, reporting that the serving cell signal measurement has fallen
below the serving cell threshold and providing information about the neighbor
cell used to generate a handover command.
[0103] Figure 10 is a flow diagram of a cell signal measurement reporting
method 1000 performed by a WTRU. In step 1005, a serving cell signal
measurement is performed. In step 1010, a neighbor cell signal measurement is
performed. In step 1015, a TTT interval is started when the neighbor cell
signal
measurement rises above a reporting range threshold. In step 1020, if the
serving cell signal measurement falls below a serving cell threshold and stays
below the threshold during a predetermined time interval, the TTT interval is
adjusted and a measurement report is transmitted during the TTT interval,
reporting that the serving cell signal measurement has fallen below the
serving
cell threshold and providing information about the neighbor cell used to
generate
a handover command.
[0104] Embodiments
1. A wireless communication method of adjusting the ranking criteria of
a serving cell associated with a wireless transmit/receive unit (WTRU), the
method comprising:
performing a signal measurement of a serving cell;
setting a serving cell hysteresis value to a first value if the signal
measurement of the serving cell exceeds a first threshold;
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setting the serving cell hysteresis value to a second value if the signal
measurement of the serving cell is less that the first threshold and is
greater
than a second threshold for a first time interval;
setting the serving cell hysteresis value to a third value if the signal
measurement of the serving cell is less than the second threshold for a second
time interval; and
adjusting the ranking criteria of the serving cell based on the serving cell
hysteresis value after being set to one of the first value, the second value
and the
third value.
2. The method of embodiment 1 wherein the serving cell signal
measurement is reference symbol received quality (RSRQ) and the first and
second thresholds are RSRQ thresholds.
3. The method of embodiment 1 wherein the serving cell signal
measurement is received signal code power (RSCP) and the first and second
thresholds are RSCP thresholds.
4. The method of embodiment 1 wherein the serving cell signal
measurement is reference signal received power (RSRP) and the first and second
thresholds are RSRP thresholds.
5. The method as in any one of embodiments 1-4 wherein the serving
cell signal measurement is used to calculate different levels of speed
associated
with the WTRU.
6. The method as in any one of embodiments 1-5 wherein the first value
is greater than the second value, the second value is greater than the third
value,
and the first threshold is greater than the second threshold.
7. The method as in any one of embodiments 1-6 wherein the first,
second and third values are signaled by a network.
8. The method as in any one of embodiments 1-7 wherein the first value
and at least one scaling factor are signaled by a network, and the second and
third values are derived from the first value using the at least one scaling
factor.
9. The method as in any one of embodiments 1-8 further comprising:
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adjusting a time value of a reselection timer located in the WTRU based on
how the signal measurement compares to the first and second thresholds.
10. The method as in any one of embodiments 1-9 further comprising:
receiving a radio resource control (RRC) message indicating at least one of
the first threshold and the second threshold.
11. The method as in any one of embodiments 1-10 further comprising:
receiving a radio resource control (RRC) message indicating at least one of
the first value, the second value and the third value.
12. A wireless communication method of adjusting the ranking criteria
of a neighbor cell associated with a wireless transmit/receive unit (WTRU),
the
method comprising:
performing a signal measurement of a serving cell;
setting a neighbor cell offset value to a first value if the signal
measurement of the serving cell exceeds a first threshold;
setting the neighbor cell offset value to a second value if the signal
measurement of the serving cell is less that the first threshold and is
greater
than a second threshold for a first time interval;
setting the neighbor cell offset value to a third value if the signal
measurement of the serving cell is less than the second threshold for a second
time interval; and
adjusting the ranking criteria of the neighbor cell based on the neighbor
cell offset value after being set to one of the first value, the second value
and the
third value.
13. The method of embodiment 12 wherein the serving cell signal
measurement is reference symbol received quality (RSRQ) and the first and
second thresholds are RSRQ thresholds.
14. The method of embodiment 12 wherein the serving cell signal
measurement is received signal code power (RSCP) and the first and second
thresholds are RSCP thresholds.
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15. The method of embodiment 12 wherein the serving cell signal
measurement is reference signal received power (RSRP) and the first and second
thresholds are RSRP thresholds.
16. The method as in any one of embodiments 12-15 wherein the serving
cell signal measurement is used to calculate different levels of speed
associated
with the WTRU.
17. The method as in any one of embodiments 12-16 wherein the first
value is greater than the second value, the second value is greater than the
third
value, and the first threshold is greater than the second threshold.
18. The method as in any one of embodiments 12-17 wherein the first,
second and third values are signaled by a network.
19. The method as in any one of embodiments 12-18 wherein the first
value and at least one scaling factor are signaled by a network, and the
second
and third values are derived from the first value using the at least one
scaling
factor.
20. The method as in any one of embodiments 12-19 further comprising:
adjusting a time value of a reselection timer located in the WTRU based on
how the signal measurement compares to the first and second thresholds.
21. The method as in any one of embodiments 12-20 further comprising:
receiving a radio resource control (RRC) message indicating at least one of
the first threshold and the second threshold.
22. The method as in any one of embodiments 12-21 further comprising:
receiving a radio resource control (RRC) message indicating at least one of
the first value, the second value and the third value.
23. A wireless transmit/receive unit (WTRU) comprising:
a receiver configured to perform a signal measurement of a serving cell;
and
a processor configured to set a serving cell hysteresis value to a first value
if the signal measurement of the serving cell exceeds a first threshold, set
the
serving cell hysteresis value to a second value if the signal measurement of
the
serving cell is less that the first threshold and is greater than a second
threshold
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for a first time interval, set the serving cell hysteresis value to a third
value if the
signal measurement of the serving cell is less than the second threshold for a
second time interval, and adjust the ranking criteria of the serving cell
based on
the serving cell hysteresis value after being set to one of the first value,
the
second value and the third value.
24. The WTRU of embodiment 23 wherein the serving cell signal
measurement is reference symbol received quality (RSRQ) and the first and
second thresholds are RSRQ thresholds.
25. The WTRU of embodiment 23 wherein the serving cell signal
measurement is received signal code power (RSCP) and the first and second
thresholds are RSCP thresholds.
26. The WTRU of embodiment 23 wherein the serving cell signal
measurement is reference signal received power (RSRP) and the first and second
thresholds are RSRP thresholds.
27. The WTRU as in any one of embodiments 23-26 wherein the serving
cell signal measurement is used to calculate different levels of speed
associated
with the WTRU.
28. The WTRU as in any one of embodiments 23-27 wherein the first
value is greater than the second value, the second value is greater than the
third
value, and the first threshold is greater than the second threshold.
29. The WTRU as in any one of embodiments 23-28 wherein the first,
second and third values are signaled by a network.
30. The WTRU as in any one of embodiments 23-29 wherein the first
value and at least one scaling factor are signaled by a network, and the
second
and third values are derived from the first value using the at least one
scaling
factor.
31. The WTRU as in any one of embodiments 23-30 further comprising:
a reselection timer, wherein a time value of the reselection timer is
adjusted based on how the signal measurement compares to the first and second
thresholds.
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32. The WTRU as in any one of embodiments 23-31 wherein the
receiver is further configured to receive a radio resource control (RRC)
message
indicating at least one of the first threshold and the second threshold.
33. The WTRU as in any one of embodiments 23-32 wherein the receiver
is further configured to receive a radio resource control (RRC) message
indicating at least one of the first value, the second value and the third
value.
34. A wireless transmit/receive unit (WTRU) comprising:
a receiver configured to perform a signal measurement of a serving cell;
and
a processor configured to set a neighbor cell offset value to a first value if
the signal measurement of the serving cell exceeds a first threshold, set the
neighbor cell offset value to a second value if the signal measurement of the
serving cell is less that the first threshold and is greater than a second
threshold
for a first time interval, set the neighbor cell offset value to a third value
if the
signal measurement of the serving cell is less than the second threshold for a
second time interval, and adjust the ranking criteria of the neighbor cell
based on
the neighbor cell offset value after being set to one of the first value, the
second
value and the third value.
35. The WTRU of embodiment 34 wherein the serving cell signal
measurement is reference symbol received quality (RSRQ) and the first and
second thresholds are RSRQ thresholds.
36. The WTRU of embodiment 34 wherein the serving cell signal
measurement is received signal code power (RSCP) and the first and second
thresholds are RSCP thresholds.
37. The WTRU of embodiment 34 wherein the serving cell signal
measurement is reference signal received power (RSRP) and the first and second
thresholds are RSRP thresholds.
38. The WTRU as in any one of embodiments 34-37 wherein the serving
cell signal measurement is used to calculate different levels of speed
associated
with the WTRU.
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39. The WTRU as in any one of embodiments 34-38 wherein the first
value is greater than the second value, the second value is greater than the
third
value, and the first threshold is greater than the second threshold.
40. The WTRU as in any one of embodiments 34-39 wherein the first,
second and third values are signaled by a network.
41. The WTRU as in any one of embodiments 34-40 wherein the first
value and at least one scaling factor are signaled by a network, and the
second
and third values are derived from the first value using the at least one
scaling
factor.
42. The WTRU as in any one of embodiments 34-41 further comprising:
a reselection timer, wherein a time value of the reselection timer is
adjusted based on how the signal measurement compares to the first and second
thresholds.
43. The WTRU as in any one of embodiments 34-42 wherein the
receiver is further configured to receive a radio resource control (RRC)
message
indicating at least one of the first threshold and the second threshold.
44. The WTRU as in any one of embodiments 34-43 wherein the receiver
is further configured to receive a radio resource control (RRC) message
indicating at least one of the first value, the second value and the third
value.
45. A wireless transmit/receive unit (WTRU) comprising:
a reselection timer;
a receiver configured to perform a signal measurement of a serving cell; and
a processor configured to set the reselection timer to a first value if the
signal measurement of the serving cell exceeds a first threshold, set the
reselection timer to a second value if the signal measurement of the serving
cell
is less that the first threshold and is greater than a second threshold for a
first
time interval, and set the reselection timer to a third value if the signal
measurement of the serving cell is less than the second threshold for a second
time interval.
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46. The WTRU of embodiment 45 wherein the serving cell signal
measurement is reference symbol received quality (RSRQ) and the first and
second thresholds are RSRQ thresholds.
47. The WTRU of embodiment 45 wherein the serving cell signal
measurement is received signal code power (RSCP) and the first and second
thresholds are RSCP thresholds.
48. The WTRU of embodiment 45 wherein the serving cell signal
measurement is reference signal received power (RSRP) and the first and second
thresholds are RSRP thresholds.
49. The WTRU as in any one of embodiments 45-48 wherein the serving
cell signal measurement is used to calculate different levels of speed
associated
with the WTRU.
50. The WTRU as in any one of embodiments 45-49 wherein the first
value is greater than the second value, the second value is greater than the
third
value, and the first threshold is greater than the second threshold.
51. The WTRU as in any one of embodiments 45-50 wherein the first,
second and third values are signaled by a network.
52. The WTRU as in any one of embodiments 45-51 wherein the first
value and at least one scaling factor are signaled by a network, and the
second
and third values are derived from the first value using the at least one
scaling
factor.
53. The WTRU as in any one of embodiments 45-52 wherein the
receiver is further configured to receive a radio resource control (RRC)
message
indicating at least one of the first threshold and the second threshold.
54. The WTRU as in any one of embodiments 45-53 wherein the receiver
is further configured to receive a radio resource control (RRC) message
indicating at least one of the first value, the second value and the third
value.
55. A wireless communication method of adjusting the ranking criteria
of a serving cell associated with a wireless transmit/receive unit (WTRU), the
method comprising:
setting a reselection timer in the WTRU to a first value;
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setting a hysteresis value to a second value;
monitoring a number of cell reselections associated with the WTRU that
occur during a predetermined time period;
monitoring mobility factors associated with the WTRU; and
if the number of cell reselections exceeds a third value, and a high mobility
factor is detected, determining whether to perform a first adjustment of the
reselection timer by multiplying the first value with a first scaling factor,
perform
a second adjustment by multiplying the second value of the hysteresis value
with
a second scaling factor, or perform both of the first and second adjustments,
to
reduce the ranking of the serving cell.
56. The method of embodiment 55 wherein the determination as to
whether or not to perform both of the first and second adjustments is based on
a
radio condition.
57. The method as in any one of embodiments 55 and 56 wherein the
first scaling factor is the same as the second scaling factor.
58. The method as in any one of embodiments 55 and 56 wherein the
first scaling factor is different than the second scaling factor.
59. The method as in any one of embodiments 55-58 wherein the first
value indicates a time for which a neighbor cell is expected to meet a cell
reselection criteria for the WTRU.
60. The method as in any one of embodiments 55-59 further
comprising:
receiving a radio resource control (RRC) message indicating at least one of
the first scaling factor and the second scaling factor.
61. A wireless transmit/receive unit (WTRU) comprising:
a receiver configured to monitor mobility factors associated with the
WTRU;
a reselection timer; and
a processor configured to monitor a number of cell reselections associated
with the WTRU that occur during a predetermined time period, set the
reselection timer to a first value, set a hysteresis value to a second value,
and
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determine whether to perform a first adjustment of the reselection timer by
multiplying the first value with a first scaling factor, perform a second
adjustment by multiplying the second value of the hysteresis value with a
second
scaling factor, or perform both of the first and second adjustments, to reduce
the
ranking of the serving cell, if the number of cell reselections exceeds a
third
value, and a high mobility factor is detected.
62. The WTRU of embodiment 61 wherein a determination as to whether
or not to perform both of the first and second adjustments is based on a radio
condition.
63. The WTRU as in any one of embodiments 61 and 62 wherein the
first scaling factor is the same as the second scaling factor.
64. The WTRU as in any one of embodiments 61 and 62 wherein the
first scaling factor is different than the second scaling factor.
65. The WTRU as in any one of embodiments 61-64 wherein the first
value indicates a time for which a neighbor cell is expected to meet a cell
reselection criteria for the WTRU.
66. The WTRU as in any one of embodiments 61-65 wherein the receiver
is further configured to receive a radio resource control (RRC) message
indicating
at least one of the first scaling factor and the second scaling factor.
67. A cell signal measurement reporting method performed by a
wireless transmitJreceive unit (WTRU), the method comprising:
performing a serving cell signal measurement;
performing a neighbor cell signal measurement;
starting a time-to-trigger time (TTT) interval when the neighbor cell signal
measurement rises above a reporting range threshold; and
if the serving cell signal measurement falls below a serving cell threshold,
adjusting the TTT interval and transmitting a measurement report before the
expiration of the TTT interval reporting that the serving cell signal
measurement
has fallen below the serving cell threshold and providing information about
the
neighbor cell used to generate a handover command.
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68. The method of embodiment 67 wherein the serving cell signal
measurement is used to calculate different levels of speed associated with the
WTRU.
69. The method as in any one of embodiments 67 and 68 wherein the
handover command is associated with at least one of an intra-frequency
handover, an inter-frequency handover and an inter-radio access technology
(inter-RAT) handover.
70. A cell signal measurement reporting method performed by a
wireless transmit/receive unit (WTRU), the method comprising:
performing a serving cell signal measurement;
performing a neighbor cell signal measurement;
starting a time-to-trigger time (TTT) interval when the neighbor cell signal
measurement rises above a reporting range threshold; and
if the serving cell signal measurement falls below a serving cell threshold
and stays below the threshold during a predetermined time interval, adjusting
the TTT interval and transmitting a measurement report during the TTT
interval reporting that the serving cell signal measurement has fallen below
the
serving cell threshold and providing information about the neighbor cell used
to
generate a handover command.
71. The method of embodiment 70 wherein the serving cell signal
measurement is used to calculate different levels of speed associated with the
WTRU.
72. The method as in any one of embodiments 70 and 71 wherein the
handover command is associated with at least one of an intra-frequency
handover, an inter-frequency handover and an inter-radio access technology
(inter-RAT) handover.
73. A wireless transmit/receive unit (WTRU) comprising:
a receiver configured to perform a serving cell signal measurement and a
neighbor cell signal measurement;
a time-to-trigger time (TTT) timer;
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a processor configured to start a TTT interval established by the TTT
timer when the neighbor cell signal measurement rises above a reporting range
threshold and adjust the TTT interval; and
a transmitter configured to transmit a measurement report before the
expiration of the TTT interval if the serving cell signal measurement falls
below
a serving cell threshold, the measurement report indicating that the serving
cell
signal measurement has fallen below the serving cell threshold and provide
information about the neighbor cell used to generate a handover command.
74. The WTRU of embodiment 73 wherein the serving cell signal
measurement is used to calculate different levels of speed associated with the
WTRU.
75. The method as in any one of embodiments 73 and 74 wherein the
handover command is associated with at least. one of an intra-frequency
handover, an inter-frequency handover and an inter-radio access technology
(inter-RAT) handover.
76. A wireless transmit/receive unit (WTRU) comprising:
a receiver configured to perform a serving cell signal measurement and a
neighbor cell signal measurement;
a time-to-trigger time (TTT) timer; and
a processor configured to start a TTT interval established by the TTT
timer when the neighbor cell signal measurement rises above a reporting range
threshold and adjust the TTT interval; and
a transmitter configured to transmit a measurement report during the
TTT interval if the serving cell signal measurement falls below a serving cell
threshold and stays below the threshold during a predetermined time interval,
the measurement report indicating that the serving cell signal measurement has
fallen below the serving cell threshold and provide information about the
neighbor cell used to generate a handover command.
77. The WTRU of embodiment 76 wherein the serving cell signal
measurement is used to calculate different levels of speed associated with the
WTRU.
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78. The method as in any one of embodiments 76 and 77 wherein the
handover command is associated with at least one of an intra-frequency
handover, an inter-frequency handover and an inter-radio access technology
(inter-RAT) handover.
79. A wireless communication method of adjusting the ranking criteria
of a serving cell associated with a wireless transmit/receive unit (WTRU), the
method comprising:
establishing a plurality of thresholds;
performing a signal measurement of a serving cell;
setting a hysteresis value to a particular value that depends upon how the
serving cell signal measurement compares to the plurality of thresholds; and
adjusting the ranking criteria of the serving cell based on the hysteresis
value after being set to the particular value.
80. The method of embodiment 79 wherein the serving cell signal
measurement is reference symbol received quality (RSRQ).
81. The method of embodiment 79 wherein the serving cell signal
measurement is received signal code power (RSCP).
82. The method of embodiment 79 wherein the serving cell signal
measurement is reference signal received power (RSRP).
83. The method as in any one of embodiments 79-82 wherein the serving
cell signal measurement is used to calculate different levels of speed
associated
with the WTRU.
84. A wireless communication method of adjusting a reselection timer in
a wireless transmit/receive unit (WTRU), the method comprising:
establishing a plurality of thresholds;
performing a signal measurement of a serving cell; and
adjusting the reselection timer based on the how the serving cell signal
measurement compares to the plurality of thresholds.
85. The method of embodiment 84 wherein the serving cell signal
measurement is reference symbol received quality (RSRQ).
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86. The method of embodiment 84 wherein the serving cell signal
measurement is received signal code power (RSCP).
87. The method of embodiment 84 wherein the serving cell signal
measurement is reference signal received power (RSRP).
88. The method as in any one of embodiments 84-87 wherein the serving
cell signal measurement is used to calculate different levels of speed
associated
with the WTRU.
89. A wireless communication method of adjusting the ranking criteria
of a neighbor cell associated with a wireless transmit/receive unit (WTRU),
the
method comprising:
establishing a plurality of thresholds;
performing a signal measurement of a serving cell;
setting a neighbor cell offset value to a particular value that depends upon
how the serving cell signal measurement compares to the plurality of
thresholds;
and
adjusting the ranking criteria of the neighbor cell based on the neighbor
cell offset value after being set to the particular value.
90. The method of embodiment 89 wherein the serving cell signal
measurement is reference symbol received quality (RSRQ).
91. The method of embodiment 89 wherein the serving cell signal
measurement is received signal code power (RSCP).
92. The method of embodiment 89 wherein the serving cell signal
measurement is reference signal received power (RSRP).
93. The method as in any one of embodiments 89-92 wherein the serving
cell signal measurement is used to calculate different levels of speed
associated
with the WTRU.
94. A wireless communication method of adjusting a reselection timer in
a wireless transmit/receive unit (WTRU), the method comprising:
establishing a plurality of thresholds;
performing a signal measurement of a serving cell; and
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adjusting the reselection timer based on the how the serving cell signal
measurement compares to the plurality of thresholds.
95. The method of embodiment 94 wherein the serving cell signal
measurement is reference symbol received quality (RSRQ).
96. The method of embodiment 94 wherein the serving cell signal
measurement is received signal code power (RSCP).
97. The method of embodiment 94 wherein the serving cell signal
measurement is reference signal received power (RSRP).
98. The method as in any one of embodiments 94-97 wherein the serving
cell signal measurement is used to calculate different levels of speed
associated
with the WTRU.
[0105] Although features and elements are described above in particular
combinations, each feature or element can be used alone without the other
features and elements or in various combinations with or without other
features
and elements. The methods or flow charts provided herein may be implemented
in a computer program, software, or firmware incorporated in a computer-
readable storage medium for execution by a general purpose computer or a
processor. Examples of computer-readable storage mediums include a read only
memory (ROM), a random access memory (RAM), a register, cache memory,
semiconductor memory devices, magnetic media such as internal hard disks and
removable disks, magneto-optical media, and optical media such as CD-ROM
disks, and digital versatile disks (DVDs).
[0106] Suitable processors include, by way of example, a general purpose
processor, a special purpose processor, a conventional processor, a digital
signal
processor (DSP), a plurality of microprocessors, one or more microprocessors
in
association with a DSP core, a controller, a microcontroller, Application
Specific
Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits,
any other type of integrated circuit (IC), and/or a state machine.
[0107] A processor in association with software may be used to implement a
radio frequency transceiver for use in a wireless transmit receive unit
(WTRU),
user equipment (UE), terminal, base station, radio network controller (RNC),
or
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any host computer. The WTRU may be used in conjunction with modules,
implemented in hardware and/or software, such as a camera, a video camera
module, a videophone, a speakerphone, a vibration device, a speaker, a
microphone, a television transceiver, a hands free headset, a keyboard, a
Bluetooth module, a frequency modulated (FM) radio unit, a liquid crystal
display (LCD) display unit, an organic light-emitting diode (OLED) display
unit,
a digital music player, a media player, a video game player module, an
Internet
browser, and/or any wireless local area network (WLAN) or Ultra Wide Band
(UWB) module.
* * ~x
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